The present invention relates to a novel metal salt of binaphthol derivative and a method for preparing the same.
2,2xe2x80x2-dihydroxy-1,1xe2x80x2-binaphthalene-3,3xe2x80x2-dicarboxylic acid, a dimer of 2-hydroxynaphthalene-3-carboxylic acid has been proposed as toning agent in preparation of azo pigments (U.S. Pat. No. 4,804,415, the content of which is incorporated herein by reference). However, little has been known about metal salts of 2,2xe2x80x2-dihydroxy-1,1xe2x80x2-binaphthalene-3,3xe2x80x2-dicarboxylic acid. Only sodium salt has been proposed as an intermediate for ionic-coupling reaction with polytetrahydrofuran.
The instant invention provides a novel metal salt of a binaphthol derivative, which is expected to have variety of uses including charge control agent for an electrophotographic toner and image fixing modifier for inkjet recording paper used in inkjet printing systems.
In another aspect of the present invention, a method for preparing the metal salt of binaphthol derivative is also provided.
Based on extensive study on preparation of 2-hydroxynaphthalene-3-carboxylic acid dimers, the inventors have found a novel metal salt was able to be obtained by reacting the dimer with a determined amount of alkali metal compound, and then subjecting the same to metal exchange reaction with a bi- or trivalent metal compound.
Accordingly, the present invention provides a novel metal salt of binaphthol derivative comprising one of following formulae 
wherein n represents an integer of 2 or 3, M represents a bi- or trivalent metal atom.
In the metal salt of binaphthol derivative represented by general formula (I), both of the two carboxylic moieties on the respective naphthalene rings form salts with the metal.
In the metal salt of binaphthol derivative represented by general formula (2), all of the carboxylic and hydroxyl moieties on the respective naphthalene rings form salts with the metal.
In-the above formulae, M represents bi- or trivalent metal such as aluminum, zinc, magnesium, calcium, strontium, barium, copper (II), iron(II), iron (III), cobalt (II), Nickel(II) and yettrium. Among them, aluminum and zinc are especially preferable.
The present invention also provides a method for preparing the metal salt of binaphthol derivative represented by formula (1) or (2).
The method for preparing the metal salt of binaphthol derivative represented by formula (1) comprises the steps of
reacting a binaphthol derivative of formula (3): 
wherein Y and Yxe2x80x2 represent carboxylic groups which may be esterified
with an alkali metal compound 1.0-2.5 times molar amount of the binaphthol derivative to give alkali metal salt of the binaphthol derivative; and
subjecting the resulting alkali metal salt to metal exchange reaction with a bi- or trivalent metal salt.
The method for preparing the metal salt of binaphthol derivative represented by formula (2) comprises the steps of reacting a binaphthol derivative of formula (3) with an alkali metal compound equal to or more than 3.0 times molar amount of the binaphthol derivative to give alkali metal salt of the binaphthol derivative; and subjecting the resulting alkali metal salt to metal exchange reaction with a bi- or trivalent metal salt.
According to the present invention, either of the metal salts of formula (1) or (2) can be selectivity obtained by controlling the molar amount of the alkali metal compound in relation to the starting material of binaphthol compound represented by formula (3).
In order to prepare the metal salt of formula (1), the molar amount of the alkali metal compound may be 1.0-2.5 times, preferably 2.0-2.2 times and more preferably about 2.0 times molar amount of the binaphthol derivative. The binaphthol derivative and the alkali metal compound are reacted to give an alkali metal salt of formula (4): 
wherein R represents an alkali metal atom.
Then the obtained alkali metal salt is reacted with a bi- or trivalent metal salt by adding an aqueous solution of the bi- or trivalent metal salt dropwise to the reaction to effect metal exchange reaction. Accordingly, the metal salt of binaphthol derivative represented by formula (1) can be obtained.
The molar amount of the bivalent metal salt used in the metal exchange reaction may be 0.5-1.4 times molar amount of the alkali metal salt of formula (4). When the metal salt is of trivalent, the amount may be 0.4-1.0 times molar amount of the salt of formula (4).
When metal salt of binaphthol derivative of formula (2) is desired, the amount of the alkali metal compound is more than 3.0 times, preferably 4.0-5.0 times and more preferably 4.0-4.2 times molar amount of the starting binaphthol derivative. The binaphthol derivative and alkali metal are reacted to give an alkali metal salt of formula (5): 
wherein R represents an alkali metal atom.
Then the obtained alkali metal salt solution is added dropwise to an aqueous solution of bi- or trivalent metal salt to effect metal exchange reaction. Accordingly, the metal salt of binaphthol derivative represented by formula (2) can be obtained.
The amount of bivalent metal salt used in the metal exchange reaction may be 2.0-2.5 times molar amount of the alkali metal salt of formula (5). When the metal salt is trivalent, the amount may be 1.5-1.9 times molar amount of the salt of formula (5).
Concentration of the aqueous solution of bi- or trivalent metal salt used in the present invention may preferably be 5-20 wt % and more preferably 5-10 wt %.
According to the present invention, either of the metal salts of formula (1) or formula (2) can be obtained selectively by controlling the molar amount of alkali metal compound in relation to the starting material of binaphthol compound.